Reuters reports that Egypt's Sinai-based jihadist group has pledged allegiance to the Islamic State (Isis) were quickly dismissed by the same militants on Twitter, after raising several doubts among experts on radical Islamists.

The news agency quoted a statement from Ansar Bayt al-Maqdis (Champions of Jerusalem) claiming that "we decided to swear allegiance to the emir of the faithful Abu Bakr al-Baghdadi, caliph of Muslims in Syria and Iraq and in other countries".

Pictures of the statement made the rounds on social media, although it was not verified by Reuters or other sources. As pointed out by Aaron Reese on the Institute for the Study of War blog, the statement does not refer to the Isis leader as Caliph Ibrahim, as per Islamic State propaganda, and it has not been posted on the official account of the group.

"This is not the first time that false statements have been attributed to Ansar Bayt al-Maqdis, and this probably false report may be related to the group's recent prominence in conjunction with the suicide attack targeting Egyptian security forces in the Sinai," Reese reports.

Ansar Bayt al-Maqdis has been operating in the restive Sinai peninsula since the Egyptian revolution against Hosni Mubarak in 2011 but stepped up its operations in the past months, since a violent Sunni Islamist uprising swept through the Middle East. While it is clear that it draws inspiration from IS, the group has targeted mainly Egyptian security forces and Israel.

"As Isis dominates the headlines, there is a general inclination to over-attribute statements to the group," Reese writes.

"This is evidenced by Egyptian media picking up reports of a "Daash" [Isis] leader named Abu Musab al-Maqdisi responding to the pledge of allegiance with 'Tips to the Mujahidin in Egypt.'

"However, this statement was published on a well-known Isis-leaning but unofficial jihadist forum and in fact pre-dates the alleged statement of allegiance by some 12 hours at least. The attribution of such statements to Isis itself and the description of the statement as a "response" is therefore spurious. "

Jihadists and IS supporters have published the alleged statement of allegiance on Twitter with a warning not to trust it until it is released from their official Twitter account.

Last month, members of Ansar Bayt beheaded three Egyptians they accused of working for Israeli intelligence and published the execution video on YouTube.

In the latest clip, the Egyptian jihadists accused the Egyptian government of President Abdel Fattah al-Sisi of collaborating with Israel to crack down on fighters in Sinai. They also pledged to track down and eliminate the local informants they rely on.

The footage was reminiscent of the execution of Western hostages at the hands of fighters with the Islamic State in Syria.